In the manufacture of integrated circuits (ICs) and other electronic devices, testing with automatic test equipment (ATE) is performed at one or more stages of the overall process. Special handling apparatus is used which places the device to be tested into position for testing. In some cases, the special handling apparatus may also bring the device to be tested to the proper temperature and/or maintain it at the proper temperature as it is being tested. The special handling apparatus is of various types including, for example, “probers” for testing unpackaged devices on a wafer and “device handlers” for testing packaged parts; herein, the terms “handling apparatus” or “peripherals” will be used to refer to all types of such apparatus. The electronic testing itself is provided by a large and expensive ATE system that includes a test head, which is required to connect to and dock with the handling apparatus. The Device Under Test (DUT) requires precision, high-speed signals for effective testing; accordingly, the “test electronics” within the ATE which are used to test the DUT are typically located in the test head which must be positioned as close as possible to the DUT. DUTs are continually becoming increasingly complex with increasing numbers of electrical connections. Furthermore, economic demands for test system throughput have led to systems that test a number of devices in parallel.
These requirements have driven the number of electrical connections between a test head and a peripheral into the thousands and the size and weight of test heads has grown accordingly. Presently, test heads may weigh from several hundred pounds to as much as two or three thousand pounds. The test head is typically connected to the ATE's stationary mainframe by means of a cable, which provides conductive paths for signals, grounds, and electrical power. In addition, the test head may require liquid coolant to be supplied to it by way of flexible tubing, which is often bundled within the cable. Further, certain contemporary test heads are cooled by air blown in through flexible ducts or by a combination of both liquid coolants and air. In the past, test systems usually included a mainframe housing power supply instruments, control computers and the like. Electrical cables couple the mainframe electronics to “pin electronics” contained in the test head. The cabling between the mainframe and the test head increases the difficulty of manipulating the test head precisely and repeatably into a desired position. Several contemporary systems now place virtually all of the electronics in the movable test head while a mainframe may still be employed to house cooling apparatus, power supplies, and the like. Thus, the increased number and spatial density of electrical contacts to be mated combined with the increased size and weight of the test head and its cable make it more difficult to accurately and repeatably position a test head with respect to a peripheral.
In testing complex devices, either individually or many in parallel, hundreds or thousands of electrical connections have to be established between the test head and the DUT or DUTs. These connections are usually accomplished with delicate, densely spaced contacts. In testing unpackaged devices on a wafer, the actual connections to the DUT or DUTs are typically achieved with needle-like probes mounted on a probe card. In testing packaged devices, it is typical to use one or more test sockets mounted on a “DUT socket board.” Herein, the term “DUT adapter” will be used to refer to the unit that holds the part or parts that make actual electrical connections to the DUT or DUTs. The DUT adapter must be precisely and repeatably positioned with respect to the peripheral in order that each of a number of DUTs may be placed, in turn, into position for testing.
Test systems may be categorized in terms of how the DUT adapter is held. Presently, in many systems the DUT adapter is fixed appropriately to the handling apparatus, which typically includes reference features to aid in accurately locating it. Herein, these systems will be referred to as “peripheral-mounted-DUT-adapter” systems. In other systems the DUT adapter is attached to the test head and positioned with respect to the handling apparatus by appropriately positioning (i.e., docking) the test head. These latter systems will be referred to as “test-head-mounted-DUT-adapter” systems. There are two possible subcategories of test-head-mounted-DUT-adapter systems. In the first subcategory, the DUT or DUTs are positioned before the test head is positioned or docked. Thus, the act of positioning the test head brings the connection elements into electrical contact with the DUT. This arrangement may be suitable for wafer scale testing, where the peripheral first positions a wafer and then the test head and DUT adapter (here a probe card configured to probe many or all of the devices on the wafer) is then positioned with respect to the wafer so that the needle-like probes contact the DUTs. In the second subcategory, the test head and DUT adapter are positioned or docked first, and this is followed by the peripheral moving DUTs in turn into position for testing as the DUT adapter remains in position.
It is to be noted that the DUT adapter must also provide connection points or contact elements with which the test head can make corresponding electrical connections. This set of connection points will be referred to as the DUT adapter electrical interface. Further, the test head is typically equipped with an electrical interface unit that includes contact elements to achieve the connections with the DUT adapter electrical interface. Typically, the test head interface contact elements are spring-loaded “pogo pins,” and the DUT adapter receiving contact elements are conductive landing pads. However, other types of connection devices may be incorporated for example for RF and/or critical analog signals. In some systems such other types of connectors are used in combination with pogo pins. The cumulative force required to compress hundreds or thousands of pogo pins and/or to mate other styles of contacts can become very high. This can be objectionable as the force required to bring the contacts into connection may be unreasonable and the force placed on the DUT adapter could cause undesirable deflections. Accordingly, alternative connection techniques, such as zero-insertion-force techniques, have been under development. For example, U.S. Pat. No. 6,833,696 (assigned to Xandex, Inc.) discloses a system having electrical contacts formed on substrates combined with mechanisms to bring corresponding contacts into engagement without placing undue force on a probe card or DUT board. It is further anticipated that in the future Micro Electromagnetic Machine (MEMS) techniques may be employed to form electrical contacts as an extension of their present use in fabricating probe cards. Overall, the contacts are very fragile and delicate, and they must be protected from damage.
In overview (more detailed descriptions will be provided further on) docking is the process of maneuvering the test head into position with respect to the peripheral for testing. In peripheral-mounted-DUT-adapter systems, docking includes properly and precisely conjoining the contact elements of the test head interface unit with their respective connection elements on the DUT adapter. In these systems, the delicate and fragile test head interface contacts must be afforded protection during the positioning and docking process. However, in test-head-mounted-DUT-adapter systems, the goal of docking is to precisely position and locate the DUT adapter with respect to the peripheral and/or DUTs. Also to be noted in test-head-mounted-DUT-adapter systems, the conjoining of the test head interface contact elements with the DUT adapter connection elements is accomplished when the DUT adapter is attached to the test head, and the contact elements are thus protected. However, the very delicate, needle-like probes of a probe card or the fragile, precisely manufactured test sockets are exposed during positioning and docking, and these too require protection.
Test head manipulators may be used to maneuver the test head with respect to the handling apparatus. Such maneuvering may be over relatively substantial distances on the order of one meter or more. The goal is to be able to quickly change from one handling apparatus to another or to move the test head away from the present handling apparatus for service and/or for changing interface components. When (as outlined above) the test head is held in a position with respect to the handling apparatus such that all of the connections between the test head the DUT adapter have been achieved and/or the DUT adapter is in its proper position, the test head is said to be “docked” to the handling apparatus. In order for successful docking to occur, the test head must be precisely positioned in six degrees of freedom with respect to a Cartesian coordinate system. Most often, a test head manipulator is used to maneuver the test head into a first position of coarse alignment within approximately a few centimeters of the docked position, and a “docking apparatus” is then used to achieve the final precise positioning.
Typically, a portion of the docking apparatus is disposed on the test head and the rest of it is disposed on the handling apparatus. Because one test head may serve a number of handling apparatuses, it is usually preferred to put the more expensive portions of the docking apparatus on the test head. The docking apparatus may include an actuator mechanism that draws the two segments of the dock together, thus docking the test head; this is referred to as “actuator driven” docking. The docking apparatus, or “dock” has numerous important functions, including: (1) alignment of the test head with the handling apparatus, including the precise alignment of electrical contacts, (2) sufficient mechanical advantage and/or actuator power to pull together, and later separate (i.e., undock), the test head and the handling apparatus, (3) providing pre-alignment protection for electrical contacts during both docking and undocking operations, and (4) latching or holding the test head and the handling apparatus together.
According to the inTEST Handbook (5th Edition© 1996, inTEST Corporation), “Test head positioning” refers to the easy movement of a test head to a handling apparatus combined with the precise alignment to the handling apparatus required for successful docking, and undocking. A test head manipulator may also be referred to as a test head positioner. A test head manipulator combined with an appropriate docking means performs test head positioning. This technology is described, for example, in the aforementioned inTEST Handbook. This technology is also described in numerous patent publications, for example a partial list includes U.S. Pat. Nos. 7,728,579, 7,554,321, 7,276,894, 7,245,118, 5,931,048, 5,608,334, 5,450,766, 5,030,869, 4,893,074, 4,715,574, and 4,589,815 as well as WIPO publications such as WO05015245A2 and WO08103328A1, which are all incorporated by reference for their teachings in the field of test head positioning systems. The foregoing patents and publications relate primarily to actuator-driven docking. Test head positioning systems are also known where a single apparatus provides both relatively large distance maneuvering of the test head and final precise docking. For example, U.S. Pat. No. 6,057,695 to Holt et al., and U.S. Pat. Nos. 5,900,737 and 5,600,258 to Graham et al., which are all incorporated by reference, describe a positioning system where docking is “manipulator-driven” rather than actuator-driven.
As previously stated, the goal of test head docking is to properly locate and position the test head with respect to the peripheral. The peripheral normally includes features, such as mounting surfaces that define a “peripheral docking plane.” The electrical contacts that connect to the DUT (and hence the DUT adapter, DUT socket board or probe card) must lie in a plane parallel to the peripheral docking plane. To facilitate docking, the docking apparatus that is mounted on the peripheral is typically located on a flat metallic plate that is attached to the peripheral such that its outer surface is parallel to the peripheral docking plane. Also the peripheral may include other reference features, such as precisely located pins or receptacles, to enable properly locating the DUT adapter.
Similarly, a “test-head docking plane” may be associated with the test head. The test head interface contact elements are typically arranged in a plane parallel to the test-head docking plane. A Cartesean coordinate system may be associated with either the test-head or peripheral docking plane such that the X and Y-axes lie in a plane parallel to the docking plane and the Z axis is perpendicular to the docking plane. Distances in the Z direction may referred to as height. It is to be noted that there may be more than one set of test head interface contact elements with the plane of each set being at a different height with respect to the docking plane. In the remainder of this document the term “docking plane” is used without a modifier it refers to the peripheral docking plane.
When properly docked, the test-head docking plane is substantially parallel to the peripheral docking plane. The process of achieving this relationship is often known as planarization and the result may be referred to as “docked planarity.” Also, when properly docked, the test head is at a predetermined preferred “docked distance” from the peripheral. Achieving docked planarity and docked distance requires three degrees of motion freedom of the test head, namely: rotations about axes parallel to the X and Y axes associated with the test-head docking plane and linear motion along the Z axis. Finally, when properly docked, the two docking planes will be aligned in the remaining three degrees of freedom corresponding to the X and Y directions as well as with respect to rotation about an axis parallel to the Z axis.
In the typical actuator-driven positioning system, an operator controls the movement of the manipulator to maneuver the test head from one location to another. This may be accomplished manually by the operator exerting force directly on the test head in systems where the test head is fully balanced in its motion axes, or it may be accomplished through the use of actuators directly controlled by the operator. In several contemporary systems, the test head is maneuvered by a combination of direct manual force in some axes and by actuators in other axes.
In order to dock the test head with the handling apparatus, the operator must first maneuver the test head to a “ready-to-dock” position, which is close to and in approximate alignment with its final docked position. The test head is further maneuvered until it is in a “ready-to-actuate” position where the docking actuator can take over control of the test head's motion. The actuator can then draw the test head into its final, fully docked position. In doing so, various alignment features provide final alignment of the test head. A dock may use two or more sets of alignment features of different types to provide different stages of alignment, from initial to final. It is generally preferred that the test head be aligned in five degrees of freedom before the fragile electrical contacts make mechanical contact. The test head may then be urged along a straight line, which corresponds to the sixth degree of freedom, that is perpendicular to the plane of the interface and peripheral docking plane.
As the docking actuator is operating (and while the dock alignment features are not imposing constraints), the test head is typically free to move compliantly in several if not all of its axes to allow final alignment and positioning. For manipulator axes which are appropriately balanced and not actuator driven, this is not a problem. However, actuator driven axes generally require that compliance mechanisms be built into them. Some typical examples are described in U.S. Pat. Nos. 5,931,048, 5,949,002, 7,084,358, and 7,245,118 as well as WIPO publication WO08137182A2 (all incorporated by reference). Often compliance mechanisms, particularly for non-horizontal unbalanced axes, involve spring-like mechanisms, which in addition to compliance add a certain amount of resilience or “bounce back.” Further, the cable connecting the test head with the ATE mainframe is also resilient leading to further bounce back effects. As the operator is attempting to maneuver the test head into approximate alignment and into a position where it can be captured by the docking mechanism, he or she must overcome the resilience of the system, which can often be difficult in the case of very large and heavy test heads. Also, if the operator releases the force applied to the test head before the docking mechanism is appropriately engaged, the resilience of the compliance mechanisms may cause the test head to move away from the dock.
U.S. Pat. No. 4,589,815 to Smith (incorporated by reference), discloses a prior art docking mechanism. The docking mechanism illustrated in FIGS. 5A, 5B, and 5C of the '815 patent uses two guide pin and receptacle combinations to provide final alignment and two circular cams. The guide pin receptacles are located in gussets that also hold cam followers which engage with the cams. To achieve a ready-to-actuate position, the cams must be fitted between the gussets such that the cam followers can engage helical cam slots located on the cams' cylindrical surfaces. Fitting the cams between the gussets provides a first, coarse alignment and also provides a degree of protection to the electrical contacts, probes or sockets as the case may be. When the cams are rotated by handles attached to them, the two halves of the dock are pulled together with the guide pins becoming fully inserted into their mating receptacles. A wire cable links the two cams so that they rotate in synchronism. The cable arrangement enables the dock to be operated by applying force to just one or the other of the two handles. The handles are accordingly the docking actuator in this case.
The basic idea of the '815 dock has evolved as test heads have become larger into docks having three or four sets of guide pins and circular cams. These are known as three-point and four-point docks respectively. FIGS. 1A and 1B of the present application illustrate a prior-art four-point dock having four gussets 116, four guide-pins 112, four complementary receptacles 112a and four circular cams 110. (This apparatus is described in more detail later.) Although such “four-point” docks have been constructed having an actuator handle 135 attached to one or more of the four cams 110, the dock shown in FIG. 1A incorporates a single actuator handle 135 that operates a cable driver 132. When the cable driver 132 is rotated by the handle 135, the cable 115 is moved so that the four cams 110 rotate in a synchronized fashion. Cams 110 engage cam followers 110a, which are attached to gussets 116. This arrangement places a single actuator handle in a convenient location for the operator. Also, greater mechanical advantage can be achieved by appropriately adjusting the ratio of the diameters of the cams to the diameter of the cable driver. In these docks, the interaction between the guide pins 112 and their corresponding receptacles 112a determines the position of the docked test head in three degrees of freedom in a plane parallel to the peripheral docking plane. As the cams 110 are rotated, the interaction between the cam followers 110a and the cam slots 129 control the remaining three degrees of freedom, namely the planarity of the test head with respect to the peripheral docking plane and the distance between the test head and the peripheral 108. When the cams 110 have been fully rotated, the gussets 116, which are attached to the peripheral 108, bear against the test head 100, establishing the final “docked distance” between test head 100 and peripheral 108 as well as the final “docked planarity” of the test head.
Other prior art docks, such as those manufactured by Reid Ashman, Inc., are similar in concept but utilize linear cams in lieu of circular cams and solid links instead of cables to synchronously drive the cams. Another scheme that utilizes linear cams but which is actuated by pneumatic elements is described in U.S. Pat. No. 6,407,541 to Credence Systems Corporation (incorporated by reference). In the '541 patent, “docking bars” serve a similar purpose to the previously described “gussets.” However, when the test head is docked, the docking bars do not bear against the unit being docked to; thus, the interaction between the cam followers and the cams solely determines the docked distance and docked planarity.
Still other variations of docks are known. For example, a partially automated dock that may be operated in either partially or fully powered modes and which incorporates cable-driven circular cams is disclosed in U.S. Pat. Nos. 7,109,733 and 7,466,122 (both incorporated by reference), both to the present assignee. A further dock configuration including solid link driven circular cams and which may be powered is described in WIPO publication WO2010/009013A2 (incorporated by reference), also to the present assignee. These docks utilize guide pins and receptacles to establish position within the plane and gussets or the equivalent to establish docked planarity and the docked distance between the test head and the peripheral.
Still another variation is described in U.S. Pat. No. 6,870,363 to Thurmaier, which is also included by reference. In this scheme docking pins are disposed upon the handling device and docking pin receivers are respectively disposed on the test head (or vise versa). In order to dock, the pins are axially inserted into the receivers, where they are captured by an arrangement of balls operated by a clamping device. All pins are captured simultaneously. Actuation apparatus may then draw the pins, and thus the test head, into a docked position.
Additionally, the docks described in U.S. Pat. Nos. 5,654,631 and 5,744,974 utilize guide pins and receptacles to align the two halves. However, the docks are actuated by vacuum devices, which urge the two halves together when vacuum is applied. The two halves remain locked together so long as the vacuum is maintained. However, the amount of force that can be generated by a vacuum device is limited to the atmospheric air pressure multiplied by the effective area. Thus, such docks are limited in their application.
U.S. Pat. Nos. 7,235,964 and 7,276,895 (both incorporated by reference) to the present assignee describe docks that use relatively large alignment pins (as illustrated in FIG. 14 of the '895 patent), which are typically attached to the peripheral. The diameter of the pins is relatively narrow at their distal ends and is larger at the interior ends. Also, two cam followers are attached to the pins near the point where they are attached to the peripheral. Camming mechanisms, employing linear cams, are attached to the test head. The distal ends of the alignment pins may be first inserted into the camming mechanisms to provide a first stage of course alignment. As the test head is urged closer to the peripheral, the larger diameter enters the camming mechanism to provide closer alignment. As the test head is further urged towards the peripherals, the cam followers eventually engage the cams, which may then be actuated to pull the two halves into a final docked position. No gussets are involved; the docked distance and docked planarity are solely determined by the interaction between the cams and cam followers. Further, it is necessary for the camming mechanisms to serve as pin receptacles, providing sufficient interaction with the pins to position the test head in three degrees of freedom parallel to the peripheral docking plane.